The present invention is used for sampling particles, particularly airborne particles (aerosols). There are many reasons for the sampling of aerosols including the assessment of air pollution in the atmosphere, indoors and in workplaces. Because the effects of aerosols on human health, materials, visibility, etc. depend on particle size, it is necessary to sample the aerosols with particle size selection in order to properly assess the effects. For example, inhaled particles beyond a certain size will not reach the pulmonary region of the human lung.
For some applications, public agencies and other organizations have adopted size-selective sampling criteria specifying sampling efficiency vs particle size. Apparatus for size-selective particle sampling generally consists of an inlet followed by a means to remove unwanted large particles from the airstream. The remaining airborne particles may then be collected on a filter or detected by an electronic sensing device.
A principal deficiency in prior samplers is excess penetration of solid particles compared to liquid particles because of particle bounce from collection surfaces. Some prior samplers attempt to minimize the problem by greasing or oiling collection surfaces. However, the grease loses its effectiveness as it becomes coated with particles. There is also the danger of the grease or oil migrating to the filter, and contaminating the particle deposit. The greased or oiled surfaces necessitate frequent maintenance that, if not done timely and properly, results in poor sampling performance. Cyclones are an exception in that they are free of particle bounce problems. However, their geometry is inconvenient for many applications.